The present invention relates to an improved racket frame, and more particularly relates to improvement in weight adjustability of a racket frame provided with string protectors attached to its head.
The head of a racket frame is generally oval in shape and has two main axes normal to each other. That is, a longitudinal axis is an extension of the longitudinal axis of the grip and passes through the center of the oval head. A lateral axis is normal to the longitudinal axis and also passes through the center of the oval head.
In general, proper different weight adjustment is applied to racket frames on market depending on the degree of skill of users.
Such weight adjustment is usually achieved during production by embedding a weight adjusting element or elements into the head or the grip. In some cases, they are secured to the head or the grip by bonding. Weight adjustment is also attained by properly designing weight balance before production.
Such weight adjustment at the stage of or before production does not allow free and subtle weight adjustment by users depending on the degree of personal skill. In addition, when secured by bonding, the weight adjusting elements are apt to fall during usage of racket frames. Such unexpected separation not only endangers users by also degrades the appearance of the racket frames.
Japanese patent application No. sho. 59-134514 proposes a new way of weight adjustment. Several weight adjusting elements, each including a band type substrate, are locally attached to the outer peripheral surface of the head of a racket frame and each weight adjusting element is held firm at the position of attachment by a string extending in tension between adjacent string holes in the head.
The above-described substrate is formed in one body with associated tubular string protectors inserted into the adjacent string holes. At formation of the face in tension at shops, the weight adjusting element is cut to a length depending on the personal preference of each user, attached to the outer peripheral surface of the head with the associated string protectors being inserted into adjacent string holes, and fixed to the position of attachment by a string extending in tension between the adjacent string holes.
There is sold in market a type of tennis racket in which string protectors solely or accompanied with a string protector band are already attached over the entire outer peripheral surface of the head during production. When the above-described new proposal is to be applied to a tennis racket of this type, the protector band has to be removed at positions of attachment of the weight adjusting elements. In addition, this proposed new way also does not allow free and subtle weight adjustment by users after formation of the face in tension.
Further, when the weight adjusting elements, each including the band type substrate, are attached to the opposite lateral sections of the head astride the lateral axis, it is necessary to displace the weight adjusting element circumferentially on the outer peripheral surface of the head for weight balance adjustment. It is also necessary to prepare weight adjusting elements of different weights, i.e. thicknesses.